An aneurysm is a dilation of a blood vessel that poses a risk to health from the potential for rupture, clotting, or dissecting. Rupture of an aneurysm in the brain causes stroke, and rupture of an aneurysm in the abdomen causes shock. Cerebral aneurysms are usually detected in patients as the result of a seizure or hemorrhage and can result in significant morbidity or mortality.
There are a variety of materials and devices which have been used for treatment of aneurysms, including platinum and stainless steel microcoils, polyvinyl alcohol sponges (Ivalone), and other mechanical devices. For example, vaso-occlusion devices are surgical implements or implants that are placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. One widely used vaso-occlusive device is a helical wire coil having windings that may be dimensioned to engage the walls of the vessels. (See, e.g., U.S. Pat. No. 4,994,069 to Ritchart et al.). Variations of such devices include polymeric coatings or attached polymeric filaments have also been described. See, e.g., U.S. Pat. Nos. 5,226,911; 5,935,145; 6,033,423; 6,280,457; 6,287,318; and 6,299,627. In addition, coil designs including stretch-resistant members that run through the lumen of the helical vaso-occlusive coil have also been described. See, e.g., U.S. Pat. Nos. 5,582,619; 5,833,705; 5,853,418; 6,004,338; 6,013,084; 6,179,857; and 6,193,728.
Typically, implantable devices include a detachment mechanism in order to be released from the deployment mechanism (e.g., attached wire). Several classes of techniques have been developed to enable more accurate placement of implantable devices within a vessel. One class involves the use of electrolytic means to detach the vasoocclusive member from the pusher. Electrolytic coil detachment is disclosed in U.S. Pat. Nos. 5,122,136; 5,354,295; 6,620,152; 6,425,893; and 5,976,131, all to Guglielmi et al., describe electrolytically detachable embolic devices. U.S. Pat. No. 6,623,493 describes vaso-occlusive member assembly with multiple detaching points. U.S. Pat. Nos. 6,589,236 and 6,409,721 describe assemblies containing an electrolytically severable joint. U.S. Patent Publication No. 20060271097A1 describes interlocking loop detachment junctions made of metal in which the loop proximal to the implantable device is degraded by the application of energy. U.S. Patent Publication No. 20060271086A1 describes flexible detachment junctions formed by covering the implantable device and a delivery device with an articulating degradable polymer.
Other forms of energy are also used to sever sacrificial joints that connect pusher and vasoocclusive member apparatus. Sacrificial connection member, preferably made from polyvinylacetate (PVA), resins, polymers, or shape memory alloys, can be used to join a conductive wire to a retention member. See, U.S. Pat. Nos. 5,759,161 and 5,846,210. Upon heating by a monopolar high frequency current, the sacrificial connection member melts, severing the wire from the retention member.
U.S. Pat. No. 5,944,733 describes application of radiofrequency energy to sever a thermoplastic joint and U.S. Pat. No. 6,743,251 describes polymeric detachment joints that are severed by the application of low frequency energy or direct current. U.S. Pat. No. 6,346,091 describes a wire detachment junction that is severed by application of vibrational energy.
In U.S. Pat. No. 4,735,201 to O'Reilly, an optical fiber is enclosed within a catheter and connected to a metallic tip on its distal end by a layer of hot-melt adhesive. The proximal end of the optical fiber is connected to a laser energy source. When endovascularly introduced into an aneurysm, laser energy is applied to the optical fiber, heating the metallic tip so as to cauterize the immediately surrounding tissue. The layer of hot-melt adhesive serving as the bonding material for the optical fiber and metallic tip is melted during this lasing, but the integrity of the interface is maintained by application of back pressure on the catheter by the physician. When it is apparent that the proper therapeutic effect has been accomplished, another pulse of laser energy is then applied to once again melt the hot-melt adhesive, but upon this reheating the optical fiber and catheter are withdrawn by the physician, leaving the metallic tip in the aneurysm as a permanent plug. See, also U.S. Pat. No. 6,277,126.
Other methods for placing implantable devices within the vasculature utilize heat releasable bonds that can be detached by using laser energy (see, U.S. Pat. No. 5,108,407). EP 0 992 220 describes an embolic coil placement system which includes conductive wires running through the delivery member. When these wires generate sufficient heat, they are able to sever the link between the embolic coil and the delivery wires. Further, U.S. Pat. No. 6,113,622 describes the use of fluid pressure (e.g., hydraulics) to detach an embolic coil.
However, there remains a need for composite detachment mechanisms as described herein.